Crowds thronged the Daley Center municipal building to catch a glimpse of the 44th US president.
There was no official explanation for his dismissal, but it is not uncommon for people called to perform jury service not to be assigned a case.
Mr Obama arrived at court on Wednesday morning and left around midday.
The former president, who was once a law professor, has a house in Chicago.
Each potential juror is paid about $17.20. Posted by Abdul